Plant trichomes: a model for cell differentiation

Key Points Analysis of the single-celled Arabidopsis thaliana trichomes has provided insights into several general cellular processes and machineries, including the function of transcription factors, cell-cycle regulation, the control of the microtubule and actin cytoskeleton, and cell-death control. Trichome patterning begins with cells that are initially equivalent. A pattern is generated through cell–cell communication between neighbouring cells, which is mediated by the movement of small MYB-like proteins that interact with a complex that comprises a MYB-like transcription factor, a basic helix–loop–helix (HLH) protein and a WD40 protein. Trichomes are polyploid, and overexpression studies and mutants enabled the analysis of how the switch from mitosis to endoreduplication is regulated and how the number of cycles is controlled. Trichome branching is controlled by at least four different pathways, which involve microtubules, cell growth or one of two genes — ANGUSTIFOLIA (which is involved in transcriptional regulation or Golgi-dependent processes) or STICHEL (which has unknown biochemical properties). The directionality of cell expansion is controlled by the actin-modulating ARP2/3 complex. Analysis of these different processes in one model cell type offers the possibility to explore how seemingly unrelated processes might be interconnected during development. During the past few years, the focus in plant developmental biology has shifted from studying the organization of the whole body or individual organs towards the behaviour of the smallest unit of the organism, the single cell. Plant leaf hairs, or trichomes, serve as an excellent model system to study all aspects of plant differentiation at the single-cell level, including the choice of cell fate, developmental control of the cell cycle, cell polarity and the control of cell shape.